Method of casting a plurality of ingots in a consumable electrode furnace

ABSTRACT

A method and apparatus for continuously casting one or more ingots by maintaining a pool of molten metal in a first ingot section that has a larger transverse cross-sectional area than the transverse cross-sectional area of the ingot mold or molds which are in open communication with said first ingot section by causing said molten metal to flow continuously from said pool into said ingot mold or molds while preventing the molten metal in said pool from freezing at the interface of said first mold section and said mold or molds. A refractory lining for said first mold section is used to prevent the molten metal from freezing.

United States Patent 1191 Luchok et al.

[ Jan. 1,1974

[75] Inventors: John Luchok, Delran; Patrick J.

Wooding, Moorestown, both of NJ.

[73] Assignee: Consarc Corporation, Rancocas,

[22] Filed: Sept. 7, 1971 [21] Appl. No.1 177,939

3,677,323 7/1972 Wahlster et al 164/252 X FOREIGN PATENTS OR APPLICATIONS 1,161,668 3/1958 France 164/281 1,057,291 5/1959 Germany 164/281 Primary Examiner-R. Spencer Annear Attrney-Arthur I-I. Seidel et a1.

[ 7 ABSTRACT A method and apparatus for continuously casting one or more ingots by maintaining a pool of molten metal [52] US. Cl. 164/52, 164/281 in a first ingot Section that has a larger transverse [51 I f Cl Bzzd 27/02 322d 1 H cross-sectional area than the transverse cross-sectional FIG! 0 Search 52, area f the ingot mold or molds are in p 273 75/10 C communication with said first ingot section by causing said molten metal to flow continuously from said pool [56] References C'ted into said ingot mold or molds while preventing the UN E STATES PATENTS molten metal in said pool from freezing at the inter- 2,310,635 2/1943 Hopkins 164/252 x face of said first mold section and said mold or molds. 2,445,670 7/1948 Hopkins 164/252 A refractory lining for said first mold section is used to 3,344,839 10/1967 Sunnen 164/82 X prevent the molten metal from freezing. 3,494,410 2/1970 Birchill et al. 164/281 X 3,669,178 6/1972 Theisen 164/50 5 Claims, 5 Drawing Figures 34/ 4 C 36; i 38* O l I 3 I 2 l; 5

\I 3 I I FM L\ 3 5a Z l 40 44 5a 40 PATENTED 1 3.782.445

JOHN L UCHOK PA TRICK J. WOOD/N6 JMFMMLM ATTORNEYS- METHOD OF CASTING A PLURALITY F INGOTS IN A CONSUMABLE ELECTRODE FURNACE This invention relates to a method and apparatus for casting ingots. More particularly, this invention relates to a method and apparatus for simultaneously melting single large electrodes'or multiple electrodes and casting multiple ingots. Still more particularly, the present invention relates to a method and apparatus for simultaneously and continuously casting a plurality of ingots from a single large electrode or multiple electrodes melted according to the electroslag process into a common slag bath.

The manufacture of ingots according to any one of several consumable electrode processes generally contemplates the melting or' remelting of an electrode into an ingot whose cross-sectional area is larger than that of the electrode. ln'commorr practice, the ratio of electrode to ingot cross-sectional area ranges up to about 80 percent. In certain instances it is desirable for the ratio of the electrode to the ingot cross-sectional area to equal or exceed 100 percent; that is, it is often desirable to manufacture an ingot whose cross-sectional area is smaller than the cross sectional area of the electrode. Unfortunately, there are certain metallurgical and economic restrictions which make the foregoing desirable result difficult to achieve. The present invention provides a method and apparatus that allows the electrode to ingot cross-sectional ratio to equal or exceed 100 percent. More particularly, the present invention allows the simultaneous casting of two-or more ingots.

The cost of ingot manufacture in the electroslag remelting or other consumable electrode processes is in part a function of a melt rate which in turn is a function of the ingot cross-sectional area. Thus, the smaller the ingot cross-sectional area, the fewer pounds per minute can be cast. Stated otherwise, the tolerable solidification rate for a given alloy is a function of the metallurgical characteristics and quality standards established by specification. As a general rule, the tolerable solidification rate decreases with the decrease in ingot cross-sectional area. Therefore, it can be stated that low melt rates result in poor furnace utilization and thus drive up the unit cost of producing ingots by conventional electroslag remelting or other consumable electrode processes.

Also, the cost of manufacturing an electrode to be used in the consumable process increases as the diameter of the electrode decreases. Consequently, the manufacture of small ingots by consumable electrode processes, and in particular the electroslag remelting pro cess, has heretofore not been widely adopted'for use in the manufacture ofingots of small cross-sectional area.

The present invention relates to a method and apparatus for overcoming the inherent difficulties in manufacturing ingots with a cross-sectional ratio equal to or in excess of 100 percent and, in particular, to a method and apparatus for the continuous simultaneous casting two or more ingots from a pool of liquid metal.

In the specific process described herein, a molten metal pool is formed as the result of melting (fusing) an electrode by the classic electroslag remeltingprocess. This process involves suspending'an electrical conduc tor in the form of an electrode so that its lower end is immersed in a liquid slag bath. The lower end of the electrode is melted by passing current through the electrode and slag in a manner such that molten metal droplets drop from the electrode through the slag layer and thus form a molten metal bath. An ingot or ingots are withdrawn from this bath.

Although described in terms of the electroslag remelting process, it should be understood. that the invention can be applied to other electrode. remelting processes such as a vacuum are or a nonconsumable process.

In particular, the invented process and apparatus for performing the process contemplates the continuous casting of one or more ingots from a pool of liquid metal. This is in contrast to the more typical process of manufacturing an ingot which merely maintains a pool of molten metal at the head of the individual ingot being formed. By having a common pool, it is possible to cast several ingots simultaneously. Still further, the present invention makes it possible to manufacture ingots having a relatively small crosssectional area using the electroslag process. Generally speaking, an ingot is considered to have a small cross-sectional area if it has a diameter of 8 inches or less. However, it should be understood that the present invention is not limited to the manufacture of small ingots. Moreover, the cross sectional form of the ingots may be any practical configuration such as round, square, rectangular, or even tubular.

In accordance with the present invention, the furnace is constructed so as to provide a first mold section whose cross-sectional area is larger than that of the ingot mold or molds which open into the first mold section. To cast an ingot or ingots, the pool ofmolten metal is first formed in the mold section of larger crosssectional area and thereafter such pool of molten metal is caused to flow into the ingot mold. It is a significant attribute of the present invention that the pool of molten metal in the first mold section is maintained in a molten metal condition. In other words, no skull which would prevent ingot removal is permitted to form in the first mold section.

As previously stated, a significant feature of the present invention is that it allows the simultaneous casting of more than one ingot, thus significantly increasing the productive capacity of an electroslag remelting furnace. By way of example, a given alloy may for metallurgical reasons be capable of only being cast as a 6 inch diameter ingot at a maximum rate of 200 pounds per hour. By designing a furnace so that four ingots are withdrawn simultaneously, it is now possible to use a large diameter electrode. Electrode manufacturing costs are thereby reduced while the total furnace output of (4 X 200) or 800 pounds per hour greatly improves the furnace productivity and thus reduces unit manufacturing costs.

There is disclosed in patent application Ser. No. 761,893 filed Sept. 16, 1968, now US. Pat. No. 3,602,623, a process for simultaneously manufacturing a plurality of ingots. The invention disclosed therein is a significant contribution to the consumable electrode method of manufacturing ingots, particularly in connection with electroslag remelting. However, it is patentably different from the present invention in that it contemplates the simultaneous melting of a plurality of ingots into a plurality of crucibles using a common power supply and a common regulator control. There is no common pool of molten metal. The present invention contemplates the manufacture of one or more ingots by causing molten metal to flow into the ingot mold or mold from a common pool.

Rheinstahl French Pat. 2,023,908 discloses a process for the production of an ingot from an electrode whose cross-sectional area is larger than that of the ingot. The furnace has a conical upper portion that is in open communication with a generally cylindrical or slightly tapered crucibles for forming the ingot. The Rheinstahl publication contemplates the manufacture of an ingot whose cross-sectional area is smaller than that of the electrode.

In the Rheinstahl publication, the pool of molten metal is conventionally maintained in the ingot mold portion of the furnace. In accordance with the present invention, the pool of molten metal is maintained in what would correspond to the upper or funnel portion of the furnace. Any attempt to operate the furnace described in the Rheinstahl publication with the molten metal pool in the upper portion would result in solidification of the molten metal adjacent the crucible walls. This would make it impossible to withdraw the ingot or, at the very least, would result in unacceptable tearing.

As previously explained, it is one of the major purposes of the present invention to provide a simple, flexible, low cost means of producing one or more ingots from a common pool of molten metal. It is too complex to add ingot molds to a furnace, but maintain individual pools of molten metal in each ingot mold. There are different problems in maintaining uniform ingot buildup, monitoring and controlling the locationof the slag-metal interface in each ingot position, and the necessity for multiple ingot withdrawal mechanisms. Moreover, the furnace system must be capable of being operated by a unsophisticated workman. Of course, any attempt to simply move the molten metal pool up into the upper, funnel like mold section as in Rheinstahl must fail because of the formation of a skull.

In accordance with the present invention a method and apparatus for maintaining a pool of molten metal in a first mold section of larger diameter than the ingot mold or molds is provided. It has been found that a thermal insulator such as a refractory lining provided in the first mold section prevents the formation of a skull and thus permits the maintenance of the molten pool in the first mold section. Stated otherwise, the provision ofa refractory lining in the first mold section allows the molten metal-slag interface to also be maintained in the first mold section. Accordingly, the first mold section can be ofa larger diameter than the ingot mold and be in communication with more than one section ingot mold.

For the purpose of illustrating the invention, there are shown in the drawings forms which are presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FIG. 1 is a transverse sectional view of an electro-slag furnace constructed in accordance with the principles of the present invention for performing the processes described herein.

FIG. 2 is an electroslag furnace constructed in accordance with the present invention for performing the processes described herein.

FIG. 3 is a plan view of the furnace illustrated in FIG. 2.

FIG. 4 is a partial sectional view illustrating another embodiment of the present invention.

FIG. 5 is a sectional view illustrating yet another embodiment of the present invention.

Referring now to the drawing in detail, there is shown in FIG. 1 a sectional view of a furnace 10, which when constructed in accordance with the principles of the present invention, provides a method and apparatus for casting ingots.

The furnace 10 includes an outer support shell 12 which houses an upper water cooled copper jacket 14 used to contain the molten metal 16 and the molten slag 18. The support shell 12 is provided with a refractory bottom 20. The refractory bottom 20 includes a replaceable refractory upper mold insert sleeve 22 which may be annular in construction. The water cooled jacket 14 together with the refractory bottom 20 and its insert 22 define what may hereinafter be referred to as a first mold section.

In direct, open communication with the first mold section through the refractory sleeve 22 is the water cooled copper ingot mold 24. It is in the copper ingot mold 24 that ingots are continuously formed and withdrawn as solidification proceeds.

An electrode 26 is reciprocably supported with its end in the molten slag 18 by conventional apparatus for that purpose, not shown. It should be noted that the electrode 26 has a cross sectional area substantially larger than the cross sectional area of the ingot mold 24 and hence the ingot 28 being formed therein. However, it should be understood that in certain circumstances it may be advantageous to use several electrodes 26 of any convenient cross sectional area simultaneously being fused under the slag 18 to form the molten metal pool 16.

The first mold section has a larger cross-sectional area than that of the ingot mold. It is in this expanded mold section that the molten slag-molten metal interface is maintained. Stated otherwise, the pool of molten metal is allowed to be formed in said first mold section.

The refractory bottom 20 together with the refractory insert sleeve 22 provide thermal insulation allowing the molten metal pool 16 to remain molten. Should any portion of the pool 16 that extends above the refractory bottom 20 become solidified, then the ingot 28 would either become jammed in the ingot mold 24, or tearing on the surface of the ingot would occur, or removal would be impossible. Thus, the refractory bottom 20 and refractory sleeve 22 sufficiently insulate molten metal from the cooling effects of the ingot mold 24 and the jacket 14 to prevent solidification at or near the interface between the ingot mold 24 and the first mold section. By preventing the solidification of the molten metal 16 in the first mold section, it is now possible to maintain a pool of molten metal as well as the metal-slag interface in said first mold section.

By way of example, but not limitation, the refractory bottom 20 and refractory sleeve 22 could be made of Zirconia (ZrO zirconia is advantageous because it can remain in contact with molten steel for long periods of time with minimum reaction tendencies. Moreover, it can also survive with minimum erosion (or solutioning) during the molten slag start and molten metal buildup period. It should be understood that the refractory bottom 20 and refractory sleeve 22 are not limited to being made of Zirconia. Other refractory products which perform the same function may be substituted. Indeed, even non-refractory materials which insulate the molten metal sufficiently to keep it in a molten condition can be substituted.

The purpose in using a replaceable sleeve 22 at the head of the ingot mold 24 is so that it can be replaced since this is the area of maximum wear.

In operation, the furnace is started in accordance with the process described below in respect to FIG. 2 or by using a water cooled copper starting plug such as is known in the industry. The electrode 26 is positioned about 3 to 4 inches from the starter plug and energized. Molten slag is poured into the first mold section until its level rises to the electrode tip. Thereafter, the melting process begins. If desired, the refractory bottom and refractory sleeve 2.2 can be preheated such as by use of a torch prior to the addition of the molten slag.

During the first few minutes, the electrode melts at a predetermined rate, thereby covering the first mold section refractory bottom 20 and starter plugs with molten metal. After the pool of molten metal is formed, ingot withdrawal is initiated and subsequently maintained at a rate equivalent to the melt off rate of the electrode. lngot withdrawal can be accomplished by any conventional means such as by lowering the ingot from a fixed mold 24 or by raising the mold from a fixed ingot. Both processes and apparatus for accomplishing the same are known and therefore need not be described in detail.

Of course, the ingot formation rate is varied depending upon ingot size (cross-sectional area) and the structure required of a given alloy. At the conclusion of the melt, electrical power is reduced or turned off while ingot extraction is allowed to proceed thus emptying the upper chamber of molten steel. The molten slag can be removed by the same process, or it can be removed by another method such as by siphoning.

The apparatus described with respect to FIG. 1 illustrates how an ingot 28 can be made with a smaller cross-sectional area than the cross-sectional area of an electrode 26.

It should be noted that metal solidification takes place entirely within the ingot mold 24. Tests have shown initial solidification of the metal takes place at the point of abutment between the refractory sleeve 22 and the water cooled ingot mold 24.

Referring now to FIGS. 2 and 3, there is shown a furnace 30 for simultaneously making several ingots using essentially the same method described in respect to the operation of the furnace 10. As shown in FIGS. 2 and 3, the furnace 30 comprises an outer shell 32 for housing an upper water cooled copper jacket 34 which is used to contain the molten metal 36 and molten slag 38. The furnace 30 is provided with a refractory bottom 40 having, by way of example, three openings which provide communication with the water cooled, copper'ingot molds 48, 50 and S2. Refractory sleeves 42, 44 and 46 are provided at the head of each ingot mold. As previously stated, such sleeves are adapted to be replaced when worn and are of annular construction. The refractory bottom 40 and refractory sleeves 42, 44 and 46 are preferably made of Zirconia, although other suitable materials may be used for providing the requisite heat insulation.

Although three ingot molds of cylindrical construction are illustrated in FIGS. 2 and 3, it should be understood that this is by way of example. The furnace could equally well be constructed with two, four or more molds. Moreover, the cross-sectional shape of the molds could be other than cylindrical, if desired.

A single electrode is shown in operating position with its tip inserted into the molten slag 38. The electrode 54 may be reciprocably supported by any conventional electrode support apparatus.

For starting the process using the furnace illustrated in FIGS. 2 and 3, starting plugs 56 are inserted into each of the ingot molds 48, 50 and 52 so that their top portion is approximately level with the top of the refractory sleeves 42, 44 and 46. One of the purposes of positioning the plugs 56 as such is to protect the refractory sleeves from attack by molten slag during start up. As shown, each of the plugs is provided with a tablelike portion standing on a pedestal within a recess designated generally as 58. This is to provide the good connection with each of the ingots to be formed by withdrawal of molten metal from the common pool 36.

After start up in accordance with the procedure described in respect to the furnace l0, ingots are formed in each of the molds by ingot withdrawal at a rate determined by the melt rate of the electrode and the alloy requirements. Thus, a plurality of ingots can be simultaneously formed from a common pool of molten metal.

Control of the rate of formation of the ingots depends substantially in part upon the position of the molten metal-slag interface. Since there is only one such interface, control problems are substantially reduced as compared with trying to maintain a molten metal slag interface in each of the ingot molds 48, 50 and 52. Since there is only one molten metal-slag interface conventional controls can be used.

Referring now to FIG. 4, there is shown a partial cross section of the junction between a water cooled ingot mold 60 and the bottom of a first mold section for containing the metal reservoir. A refractory sleeve 62 and refractory bottom 64 are provided as in the embodiment illustrated in FIGS. 1 and 2. In addition, a graphite sleeve 66 is fitted into the wall of the ingot mold 60 in abutment with the refractory sleeve 62.

The purpose of using the graphite sleeve 66 is to take advantage of its low friction qualities. Such a sleeve would improve the surface quality of the ingot being formed in the mold 60. The sleeve 66, however must be cooled since carbon will dissolve into steel if it is allowed to get too hot. For this reason, the sleeve 66 is relatively thin and is positioned in a channel formed in the wall of ingot mold 60 so that it is cooled.

In the event the alloy being cast can tolerate direct exposure to carbon, such as a copper alloy, then the refractory sleeve 62 or even the refractory bottom 64 could be made of graphite.

FIG. 5 illustrates apparatus for yet another embodiment of the inventive concept. In this embodiment the entire first mold section consists of a water-cooled structure 70. Stated otherwise, the bottom 72 of the upper mold section is also water cooled even in the area adjacent to the ingot mold 74.

In operating a furnace to produce a continuously cast ingot 76 by withdrawing it from the pool of molten metal 78 which is maintained in the first mold section by fusing the electrode 82 in the slag bath 80, the molten metal is prevented from solidifying by taking advantage of the thermal insulating properties of slag. Thus, at start up, a thin layer of slag 84 is initially formed in the bottom of the first mold section and allowed to freeze. Thereafter, the formation of the ingot 76 proceeds as previously described. The result is that the thin layer of slag 84 acts as a thermal insulator for preventing the molten metal from solidifying in the expanded first section.

Although each of the embodiments illustrated and described herein have contemplated vertical extraction of the ingot r ingots, the invention is not restricted to that configuration. The processes described herein could equally well be used for horizontal extraction of an ingot or ingots.

Although the first mold section and the ingot mold or molds are preferably made of water cooled copper, it should be understood that water cooled steel or other known types of molds that are compatible with the process could be used. Still further, the process is not limited to the use of consumable electrodes. It is contemplated that nonconsumable electrodes or other methods of melting molten metal in the first mold section could be used with equal facility.

Furnaces operated in accordance with the processes described herein may be used either for continuous casting or for the manufacture of individual ingots. Electroslag remelting would be somewhat slower than known processes for continuous casting, but the result is a better product. Better quality alloys result when they are permitted to solidify at a slower rate. Such slower solidification rates occur because the slag blanket on top of the molten metal helps maintain heat in the pool of molten metal. Moreover, the slag blanket prevents freezing from the edge of the pool of molten metal at the slag-metal interface.

As previously indicated, one of the major advantages of the apparatus and method described herein is that multiple ingots can be made from a common pool of molten metal. The process permits the use of electrodes melting at a relatively high rate while the ingots are being cast at a relatively slower rate. Stated otherwise, this means that the rate of casting an ingot is not strictly controlled by the rate at which the molten metal pool is being formed.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

We claim:

1. A method of casting a plurality of ingots in a consumable electrode furnace such that the ratio of the cross sectional area of the consumable electrode to the total cross sectional area of the ingots is equal to or exceeds percent, said furnace comprising a first mold section and a plurality of ingot molds in direct communication with said first mold section, said first mold section having a larger cross-sectional area than the total cross-sectional area of the ingot mold, comprising the steps of inserting the tip of an electrode having a crosssectional area at least as large that of the total crosssectional area of the ingot molds into the first ingot mold section, fusing the electrode to form a pool of molten metal in the first mold section of the furnace, cooling said first mold section and said ingot molds, maintaining the pool of molten metal in said first mold section while simultaneously fusing said electrode and casting ingots in each of said ingot molds, and preventing said molten metal in said pool from freezing at the interface between said first mold section and said ingot molds.

2. A method of casting a plurality of ingots in accordance with claim 1 including forming said pool of molten metal withinsaid first mold section by fusing the electrode under slag.

3. A method of casting a plurality of ingots in accordance with claim 1 including thermally insulating said consumable electrode furnace at the interface between said first mold section and said ingot molds to prevent said molten metal in said first mold section from freezing.

4. A method of casting a plurality of ingots in accordance with claim 3 wherein said furnace is thermally insulated at said interface by lining the interface with a refractory material.

5. A method of casting a plurality of ingots in accordance with claim 4 wherein said refractory material is zirconia. 

1. A method of casting a plurality of ingots in a consumable electrode furnace such that the ratio of the cross sectional area of the consumable electrode to the total cross sectional area of the ingots is equal to or exceeds 100 percent, said furnace comprising a first mold section and a plurality of ingot molds in direct communication with said first mold section, said first mold section having a larger cross-sectional area than the total cross-sectional area of the ingot mold, comprising the steps of inserting the tip of an electrode having a cross-sectional area at least as large that of the total cross-sectional area of the ingot molds into the first ingot mold section, fusing the electrode to form a pool of molten metal in the first mold section of the furnace, cooling said first mold section and said ingot molds, maintaining the pool of molten metal in said first mold section while simultaneously fusing said electrode and casting ingots in each of said ingot molds, and preventing said molten metal in said pool from freezing at the interface between said first mold section and said ingot molds.
 2. A method of casting a plurality of ingots in accordance with claim 1 including forming said pool of molten metal within said first mold section by fusing the electrode under slag.
 3. A method of casting a plurality of ingots in accordance with claim 1 including thermally insulating said consumable electrode furnace at the interface between said first mold section and said ingot molds to prevent said molten metal in said first mold section from freezing.
 4. A method of casting a plurality of ingots in accordance with claim 3 wherein said furnace is thermally insulated at said interface by lining the interface with a refractory material.
 5. A method of casting a plurality of ingots in accordance with claim 4 wherein said refractory material is zirconia. 